Frequency stabilizing system



Jam 11, 1929. R. A. HEISING ET AL 1,717,030

FREQUENCY STABILIZING SYSTEM Filed Feb. 27, 1925 Rax I" Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISING, OF MILLBURN, AND GUSTAVE C. DE COUTOULY, OF CHATHAM,

NEW JERSEY, ASSIGNORS, BY MESNE ASSIGNMENTS. TO WESTERN ELECTRIC COM- PANY, INCORPORATED, A CORPORATION OF NEW YORK.

FREQUENCY STABILIZING SYSTEM.

Application filed February 27, 1925.

This invention relates to frequency stabilizing systems and more particularly to means for preventing undesired variations in the frequency of an oscillation generator.

It has been found that when a space discharge tube oscillation generator is coupled to a space discharge repeater, any change in the inherent reactance between electrodes of the repeater will cause variations in the frequency of the oscillations produced by the oscillator. This is particularly true when an element of the oscillator resonant. circuit, which in general serves to determine the frequency of the oscillations generated, is more or less directly connected to electrodes ot the repeater tube. In this instance, the repeater reactance becomes an element of the resonant circuit.. and changes in this reactance tend to vary the tuning of this circuit and consequently the frequency of the oscillations generated in the oscillator,

One cause of variations in the inherent reactance between electrodes of a repeater the changes in the energy supplied to the repeater. The ellect. of the repeater in causing changes in frequency of an oscillator when connected as above mentioned, will therefore be particularly troublesome in a system designed to operate at a plurality of power levels. Another factor which may change the effective reactance of the repeater is a change in frequency of the waves supplied thereto.

It is an object of this invention to compensate for changes in inherent reactance of a wave Vtranslating device coupled to an oscillation generator.v

Another object. is to compensate for changes in the inherent capacity of a wave translating device coupled to an oscillatory circuit which changes tend to vary the tuning of the circuit.

An additional object is to neutralize the effect of changes in the reactance of a space discharge tube caused by changes in current or the frequency of waves supplied to the tube.

One feature of the invention is a constant reactance network, including variable reactance elementsv` one of which is a space discharge tube, the reactance of which varies inversely as that of the remaining elements of the network.

Serial No. 11,946.

An additional feature is an arrangement which has a reactance characteristic, which changes with load and with frequency in inverse proportion to corresponding changes in the reactance of a space discharge tube under similar conditions.

A further feature is a device, including a frequency stabilizing means and a switchlng means, for simultaneously varying the power` applied to a rep .ater and adjusting a compensating reactance in accordance with the change in power.

The principle upon which the present invention is based is that of compensating for the variation in reactance of a path traversed by electric waves, by a second path properly related thereto and having a reactance which is caused to change inversely with vthat of the first mentioned path. rl`he resultant reactance of the network, formed by the two paths, thus remains substantially constant.

The invention finds practical application in systems of space discharge tubes, particularly systems in which an oscillation generator is coupled to a repeater or other similar device which has a react-ance that varies with the load or frequency of the impressed waves.

According to this invention, a path is provided, in suitable relation to a space discharge tube coupled to an oscillator, and so designed that its change of reactance is, at all times, substantially the complement of the change of reactance of the tube. In practice, the path may include reactive means, for example, a condenser and an inductance, properly proportioned to produce the result mentioned. In order to extend the range of loads for which the path may fully compensate for changes of repeater reactance, there is provided a switch which functions to alter the character of the com. pensation path at the same time that it varies the power applied to the repeater, as the load is changed from one Value to another.

The invention, which will now be described in detail to completely disclose its Vmode of operation and the additional features, objects and advantages thereof, is i]- lustrated as embodied in a radio telegraph transmitting system.

The one figure of the drawing illustrates a radio telegraph system that includes the frequency stabilizing arrangement of the invention.

The radio telegraph system, shown in the drawing, includes three oscillation generators 10 associated, by means of filters 11,

with a common circuit 12, through whichA waves are supplied to amplifiers 13 and 14, connected in tandem. Amplifier' 14 is coupled to an oscillation generator 15, supplying energy to a power amplifier 1G, which has its output circuit coupled to an antenna 17. The waves supplied by the oscillators 10 are individually controllable by means of keys 18 so that a plurality of signal messages may be transmitted simultaneously by the system. Independence of signals is maintained by adjusting oscillators 10 to produce waves of different frequencies. Filters 11 are each designed to exclude waves, other than those of desired frequency produced by the associated oscillator 10, from the common circuit 12. The circuit 12 is coupled to the amplied 13 by a two-winding transformer 19. This transformer is dcsigned to efficiently transmit waves of the frequencies passed by the filters 1l. from the oscillators 1() to the amplifier 13. These frcqueneies are preferably all within the audible range. The amplifier 13 may consist of space discharge tubes arranged in balanced circuits for push-pull operation, as shown, for example, in U. S. Patent No. 1,128,292. February 16, 1915, to Colpitts. Amplifier 1st may also be of the space discharge tube type having its plate, or anode-cathode circuit, connectedfto the leads 20 and 21, the anode being preferably connected to lead 2O and the cathode to lead 21. By this ar ungemein, waves supplied from the amplifier 14 will be caused to modulate the 4oscillations generated in the space discharge tube oscillator 15. Y

The oscillation generator 15 which is of the type disclosed in Colpitts patent 1,62% 537 of AprilV 12, 1927, comprises a space disT charge tube 22 having an input circuit, connected to its control electrode and cathode, and an output circuit, connected to its anode and cathode, a feed-back path connected to its anode and control electiode, and a space current supply path also connected to its anode and cathode.

The input circuit comprises two branches. One branch extends from the grid through the condenser 35, condenser-s 38 to the cathode and across the space within 'the tube to the grid. The other branch includes a high frequency choke coil 23 in series with a potentiometer resistance 24, the secondary of transformer 37 and the space within the tube. Resistance 24 is supplied with direct current from a rectifier 25 which is in turn supplied with current through a transformer 26 connected to an alternating current source, herein shown, by way of example, as a generator' 27.

Space current is supplied to the tube 22 from the rectifier 25. The space current circuit includes the choke coils 32, 31 and 30, an adjustable portion of coil 29, coil 2S anode of tube 22, the space path between anode and cathode within the tube, the secondary winding of transformer 37 and resistance 33.

The alternating current output path of tube 22 extends from the anode through choke coil 28, coil 29 shunted by the condensers and 3G, condensers 3S, in shunt to the secondary of transforn'ier 37, to the cathode and across the space within the tube to the anode.

Choke coil 32 cooperates with condenser 3ft to suppress undesired variations in the output current from rectifier 25, whereby they are prevented from producing undesired variations in the oscillatory currents. Choke coil 3l is designed to have high impedance for waves of signal frequency transmitted from amplifier lll and prevents diversion of the waves from the input electrodes of tube 22 to the space current supply path of tube 22. Coil prevents the passage of high rfrequeney lwaves through the anode-cathode path of amplifier 14 and the space current supply path of tube 22.

The potential across potentiometer resist-- ance 2st maintains the control electrode of tube 22 at a suitable average negative potential with respect to the cathode. Potentiometer resistance 33 is arranged in shunt to the space path of tube 22 and functions to maintain a continuous flow of current through resistance 24, regardless of variation in the impedance of the space path of tube 22.

An oscillatory circuit, comprising adjustable inclut-tance 29, adjustable condenser 35 and fixed condenser 36, is suitably connected to the electrodes of tube 22. rf'his circuit in general determines the frequency of the oscillations established in the generator, including the tube 22. The frequency of these oscillations may beA varied by adjusting the inductance 29. The alternating potential difference at the terminals of condenser 35 is impressed upon the input electrodes of tube 22 and is adjustable to a suitable value by variation of the condenser capacity.

The cathode of tube 22 is heated by current from the secondary winding of transformer 37. The primary winding of the transformer is connected to the generator 27. rlhe midpoint of the secondary winding is connected to ground and its opposite halves are shunted by condensers 33 of equal capacity and low impedance to high frequency waves.

As thus far described, the high frequency oscillations established in generator 22 are modulated in accordance with the amplified waves in the output circuit of amplifier 14.

Connected to the condenser 3G, of the os- 'cillatory circuit 29, 35-36, is a coupling path including a condenser 39, in series with resistances 40 and 40. The fluctuations of potential difference of the terminals of condenser 3G, produced by the modulated waves, in the oscillator are transmitted to the coupling path and thence to the input electrodes of tube 44 over the following path: the lead including contact 42 of switch 43 to the grid of the amplifier, across the space within the tube to its cathode, condensers shunting the secondary of transformer 37', and resistance 4G.

It is to be noted that the resistance 40 is common to the high frequency output circuit of tube 22 and the input circuit of tube 44 of power amplifier 16. The voltage generated in this resistance by high frequency waves is applied across the control electrode and cathode of tube 44.

It is further important to note that the condenser 3G, forming an element of the resonant circuit of the oscillator 15, is shunted by two high frequency paths, one includingr the condenser 39, resistance 40, and resistance 40, and the other comprising the space path within tube 44 in series with resistance 46. Substantial inherent capacity will ordinarily be present between these electrodes of tube 44, especially in a tube designed for high power and its influence upon the resonant circuit of oscillator 15 may produce undesired effects, which will be described subsequently more in detail.

Further description of the circuit arrangement of amplifier 16 will now be. given. The control electrode and cathode of the tube 44 are connected to ai path including the condenser 45 adapted to prevent the production of parasitic oscillations in the amplifier circuits. This condenser renders the input path of tube 44 capacitively reactive for all frequencies at which detrimental oscillations might otherwise be generated. The function of this condenser is to so shift the phase of the energy fed back relatively to that traversing the input circuit so that sustained oscillations are not produced. rIhe input circuit of tube 44 includes a resistance 4G which is also common to its space current circuit. y

The space current circuit may be traced from the anode through inductance 47, choke coils 48 and 49, rectifier 50, resistance 46, secondary winding of transformer 37, to the cathode. The amplifier output circuit is grounded at a point between the rectifier 50 and resistance 4G.

A filter 51, for suppressing ripples in the rectified current, is connected in shunt to the rectifier 50. Choke -coil 48 is designed to impede high frequency waves to effect their exclusion from the rectifier 50. Choke coil 49 cooperates with filter 51 in smoothing out variations in the current supplied to the space path of tube 44.

Current for heating the cathode of tube 44 is supplied by means identical with that described in connection with tube 22.

A resonant circuit including adjustable inductance 47 and an adjustable tuning condenser 52 is connected to the anode and cathode of amplifier 16 and is coupled to the antenna circuit 17 by an adjustable coupling condenser 53. A blocking condenser 54 is provided to exclude direct current from the resonant circuit, and a choke coil 55 is provided to reduce the direct current potential across the coupling condenser 53, to thereby permit the use of a condenser which is simple in design and relatively inexpensive to manufacture. This choke coil, however, is of high impedance for high frequency waves and accordingly waves of this frequency at high voltage are impressed across the coupling condenser 53, whereby the energy thereof is supplied to the antenna and radiated. The antenna circuit includes a loading inductance 56 in series with the coupling condenser' 53 and is connected to ground.

Themodulated waves supplied to the input circuit of tube 44 are amplified and transmitted to the resonant circuit 47-52, and thence through the coupling condenser 53 to the antenna 17, in a manner now well understood. y

By means of switch 43, a variable inductance may be connected, in steps, in series with variable capacity 58, tonthe control electrode and cathode of tube 44 and, consequently, substantially in shunt to condenser 36. The inductance 57 and condenser 58 have contacts corresponding to contacts upon the resistance 40 so that their values may be adjusted in accordance with the valve of the resistance 40V included in the input circuit of tube 44, and hence in accordance with theload supplied thereto.

It has been found that when the load upon tube 44 exceeds a given value, or changes between certain values, the effective reactance, namely, the capacity between its control electrode and cathode, undergoes a variation which reacts upon the resonant. circuit of oscillator 15 tending to change the frequency of the waves generated. The path including inductance 57 and condenser 58 is provided to compensate for these changes in reactance of tube 44. It functions to maintain the reactance of the resonant circuit, and hence the frequency of the oscillator substantially constant for different loads applied to the amplifier 44, as Well as for Waves of different frequencies supplied by thev oscillator 15. 4

By properly proportioning the condenser 58 and the inductance 57, the reactance of they path in which they are included may be caused to change with frequency in such manner that'the change Will be substantially equal and opposite to the change of reactance With frequency in the path between the control electrode and cathode internally of tube 44. In other' words, the condenser-inductance combination 58, 57 is designed to have a reactance-frequency characteristic Which is complementary to that of the control electrode-cathode path of the discharge tube 44.

The proper proportions may be determined by adjusting switch 43 to the desired load contact and by subsequently manipulating adjustable inductance 57 and adjustable condenser 58. However the inductance of the elements of coil 57 and the capacity of the elements of condenser 58 may be predetermined and fixed in value. In order that the compensation for reactance change may be substantially correct for different loads applied to the amplifier 44, the switch 43 is arranged to change the values of inductance 57 and condenser 58 simultaneously with changes of load upon the amplifier.

In radio signaling systems, this invention enables the frequency of carrier Waves to be readily maintained Within given limits of variation and hence reduces the proba-bility of interference With other signaling stations.

Although the invention is herein described in connection with a radio telegraph transmitter, it will be readily evidentthat it need not be limited thereto, but may be applied to numerous other arrangements which will readily occur Vto persons skilled in the art.V

The invention is therefore to be limited only as indicated by the scope'of the appended y claims.

What is claimed is:

l. In a. space discharge tube system, a plurality of space discharge tubes in tandem, means including one of said tubes for generating oscillations, thc'other 'of said tubes having inherent rcactance Which is variable with frequency and tends to cause changes in the frequency of generated oscillations, and means for compensating said reactance changes to maintain the frequency of said oscillations substantially constant.

2. In a system of space discharge tubes, a plurality of space discharge repeated in tandem, means including one of said tubes for generating oscillations, another of said tubes havingwiriable inherent reactance adapted path in shuntto Velectrodes of said second to affect the frequency of the generated osc1llat1ons,and means including an adjustable mentioned tube for preventing reactance Variation from changing the frequency of oscillations generated.

3. In a system of space discharge tubes, a plurality of space discharge repeaters in tandem, means for generating oscillations in one of said repeaters including a resonant circuit, another of said repeaters including electrodes having reactance variable with frequency, said electrodes beingin substantial shunt'to a portion of said resonant circuit, and means, also in shunt to said portion, having a reactance change with frequency substantially equal and opposite to that of said tube.

4. In a system of space discharge tubes, a plurality of space discharge repeaters in tandem, means for generating oscillations in one of said repeaters including a resonant circuit, the other of said repeaters including electrodes having reactance changeable with frequency, said electrodes being in substantial shunt to a portion of said resonant circuit, and means, also in shunt to said portion, comprising an adjustable reactance for compensating for change in reactance of said tube. y

5. A radio transmitting system including, a space discharge tube arranged to generate oscillations, a secondspace discharge tube arranged to amplify the generated oscillations, and means, for preventing the second tubeV from causing changes in the frequency off oscillations generated, comprising a path in shunt to said second tube including an an inductance and a capacity.

6. In 'a radio transmitting system, a space discharge tube arranged to generate oscillations, a second space discharge tube arranged to amplify the generated oscillations, and means for preventing the second tube from causing changes in the frequency of oscillations generated, comprising a path in shunt to said second tube, including an inductance and a capacity in series.

7. In a radio transmitting system, a space discharge tube oscillator, a space discharge tube amplifier, means, for coupling said oscillator to said amplifier, comprising a potentiometer switch, for controlling the power supplied to said amplifier and having contacts for simultaneously connecting to said Vamplifier and said oscillator a path having a said inherent capacity being changeable both with the frequency and the power of Waves supplied to the amplifier' and being substantially in shunt to a portion of said resonant circuit, and means, controllable by a power adjusting switch and including a condenser and inductance in series, for providing a capacity reactance which added to the reactance of said tube produces a resulting rcactance which is substantially constant for a plurality of loa-ds and a plurality of frequencies.

9. In a radio transmitting system, an antenna, a. space discharge amplifier, including electrodes, coupled thereto, a space discharge oscillator arranged to supply oscillations modulated in accordance With a plurality of signals, to said amplifier, a condenser, in shunt to electrodes of said amplifier, to prevent undesired oscillations therein, and

means, in shunt to said condenser, to compensate for changes in rcactancc between said electrodes.

10. In combination a resonant circuit, a device connected thereto, having a reactance characteristic Which varies with frequency and thereby tends to materially vary the tuning of said circuit, and means comprising inductance and capacity connected to said circuit and having a reactance-frequency characteristic substantially complementary to the reactance-frequency characteristic of said device to render negligible the effect thereof upon said circuit.

In Witness whereof, We hereunto subscribe our names this 24th day of February, A. D. 1925.

RAYMOND A. HEISING. GUSTAV'E CHARLES DE COUTOULY. 

